Generally, an LED light source constructed by combining an LED device with a resin containing a phosphor that absorbs a portion of the light emitted from the LED device and emits light at a different wavelength has had the problem that the chromaticity of the LED light source varies due to such factors as variations in the wavelength of the LED device itself and variations in phosphor content.
In view of this, an attempt has been made to suppress the variation of the chromaticity of the LED light source by varying the amount of the resin used to seal the LED device (refer, for example, to patent document 1).
FIG. 16 is a cross-sectional view of the above prior art LED light source.
In the LED light source 210 shown in FIG. 16(a), the LED device 211 is mounted on a substrate comprising a base material 212 and conductive interconnections 213, and is electrically connected to the conductive interconnections 213 via bonding wires 214. The interior space enclosed by a reflective frame 215 mounted on the substrate is filled with a seal material. The seal material is cured by allowing phosphors 216 to settle to the bottom while leaving the portion thereabove filled only with a transparent resin 217.
FIG. 16(a) shows an example in which the transparent resin 217 in the upper part has been ground until target chromaticity is reached in the chromaticity adjustment process. In the example of FIG. 16(a), the initial resin surface position 218 has been reduced to the position 219 by grinding the resin surface. In this case, since light is confined within a narrower space (in the transparent resin), the light undergoes many more reflections, and the probability of the phosphors 216 being struck by the light from the LED device 211 increases, thus increasing the wavelength conversion rate. As a result, the chromaticity of the LED light source 210 is adjusted from the blue to yellow regions.
In the LED light source 220 shown in FIG. 16(b), the same parts as those of the LED light source 210 shown in FIG. 16(a) are designated by the same reference numerals. FIG. 16(b) shows an example in which the initial resin surface position 218 has been raised to the position 221 in the chromaticity adjustment process by further applying a resin over the initial surface. In the example of FIG. 16(b), since the amount of resin is increased, the light passes through a wider space (in the transparent resin), and the probability of the phosphors being struck by the light from the LED device 211 decreases, thus decreasing the wavelength conversion rate. As a result, the chromaticity of the LED light source 220 is adjusted from the yellow to blue regions.
In this way, the chromaticity can be adjusted by simply increasing or decreasing the amount of the transparent resin. However, in applications that impose limitations on the external shape of the LED light source, it has been difficult to increase or decrease the amount of the transparent resin. Furthermore, when grinding is performed, the LED light source may be damaged due to the applied force or scratches, leading to problems such as a break in the wire bonding or scratches on the reflective frame.
Further, with the prior art chromaticity adjustment method, the color temperature of the light emerging from the LED light source may vary depending on the angle of emergence. That is, the prior art has had the problem that the light from the LED device, when viewed straight on, for example, appears bluish, but as the viewing angle is changed, the light appears yellowish.
Patent document 1: Japanese Unexamined Patent Publication No. 2004-186488 (page 2, FIG. 1)